Actuator for bucky diaphragms



Patented Sept. 21, 1954 2,689,916 ACTUATOR FOR BUCKY DIAPHRAGMS Robert R. Lohman, Amelia, and Orlestus R. Brenner, Bridgetown, Ohio, assignors to The Liebel- Flarsheim Company, Cincinnati, Ohio, a corporation of Ohio Application May 3, 1952, Serial No. 285,864

12. Claims. 1

This invention relates to diaphragms which are employed for screening secondary radiations from a photographic film in X-ray photography. The invention is directed particularly to an improved actuator through which the diaphragm is moved over the photographic film during an X- ray exposure.

A conventional diaphragm, termed a Bucky diaphragm from the name of its inventor, consists of a plurality of thin strips of material which are opaque to X-rays and which are arranged, on edge, in spaced relationship to one another. The diaphragm is interposed between the subject to be X-rayed and the photographic film or plate. Primary radiations generated at the Xray tube pass through the subject and through the diaphragm to impinge upon the photographic film or plate, the slits of the diaphragm through which the X-rays may pass being angulated to coincide with the diverging stream of X-rays generated at the tube. However, in passing through a subject, some X-rays are scattered or deflected, thereby producing so-called secondary radiations which would blur the image on the photographic plate if they were unobstructed. It is the function of the Bucky diaphragm to screen such secondary radiations from the photographic medium; this result is accomplished because the grid or diaphragm permits the direct radiations to pass through its slits but it excludes radiations which approach it along paths outside of the angle of acceptance delineated by its slits.

The strips of the diaphragm which are opaque to X-ray would cast their shadows onthe film if the diaphragm were stationary during an X-ray exposure. To avoid this result, it is conventional practice to move the diaphragm over the surface of the film during the exposure period. An actuator is employed for this purpose.

Some Bucky mechanisms are of the single pass type, in which the diaphragm moves in one direction throughout the entire exposure period, the movement commencing just before the beginning of the exposure and terminating just after the end of the exposure period. More recently, so-called reciprocating Bucky mechanisms have been developed; in these devices the diaphragm is shuttled back and forth in opposite directions throughout the entire exposure, however long a period of time it might require. A single-pass actuator mechanism is disclosed in United States Patents to Flarsheim, No. 1,945,499 and 2,147,601 while reciprocating Bucky mechanisms are disclosed in Gieringer et a1. United States patent application Serial No.

2 71,074, now issued as United States Patent No. 2,591,536 dated April 1, 1952, and Arthur G. Billin United States Patent application Serial No. 272,658.

In both types of mechanisms, it is highly desirable if not requisite that the Bucky diaphragm once placed in motion in a given direction, he moved at a substantially uniform rate of speed, and that the same rate of speed be obtained in subsequent usage of the apparatus under the same setting or conditions. The necessity for this requirement is brought about because the X-rays are produced at the tube as pulsations, and these rays must pass through the slits in the diaphragm. If an X-ray pulsation happens to occur just when the X-ray opaque strips of the diaphragm reach the same relative position that other opaque strips of the diaphragm occupied during preceding pulsations, then the strips, though actually in movement, will cast shadows on the film just as though they were stationary, and the resultant photograph will be imperfect. A condition such as the one just noted is known in the art as synchronism; a non-synchronous condition is one in which the diaphragm is advanced in one direction, or moved in both directions at such rate or rates in relation to the X- ray pulsations and grid strip spacings that 00- incidence of strip positions with pulsations will not occur repeatedly during an exposure to such an extent that discernible or undesirable shadows will appear upon the photograph. Synchronism is avoidable by causing the diaphragm to be moved at a rate of speed which does not bear an integer or simple submultiple relationship to the pulsations of the X-ray tube, but it is apparent that if the velocity varies appreciably while the diaphragm is being moved in a given direction, the non-synchronous conditions may prevail during a part of its travel, while synchronous conditions may prevail during other parts of the travel because of velocity variation. and the net photographic results will be imperfect.

From these considerations it is apparent that the actuation of a diaphragm requires a motor mechanism of one type or another which imparts a constant speed of movement to the diaphragm each time that it is energized, or a control mechanism which is capable of governing the speed of movement regardless of variations which may occur in the performance of the motor mecha nism, and that either or both of these instrumen talities must be consistent and reliable in their performance throughout prolonged usage of the apparatus. It is also desirable that the rate of movement of the diaphragm be adjustable in order to accommodate the apparatus for use under conditions which may vary from one installation to another, or from one type of exposure to another within a single installation.

The principal objective of this invention has been to provide a simple and" reliable Bucky actuator which can-be used to obtain'a substantially uniform movement of a Bucky diaphragm. The invention, more particularly, is directed to an in- "'10 expensive mechanism which canbe fabricated without great regard for high precision in the machining of its parts butwwhich is'neve'r'itheless capable of providing uniformitvof speed in the travel of a diaphragm and=which is alsocon- "5 veniently adjustable so that it may be set to produce a desirable or predetermined "rateof travel.

Briefly, the apparatus of the present'invention embodies a motor mechanism in the form of a 0 solenoid; thrustorior the like which, wheneenergized, exertsa force which 'is IefiB'CtiVe tOI. move a diaphragm in-one direction; a fluid cylinder and piston, one or the other of which is operatedzin response to motor actuation sovas to' pncdu'ce a compression'of a control fiuidtand 'thereby'provide a force whichis'counteractive to :the motor -force, and a governor in theiformpfaa*porous *mezhbrane through which movement of fluid. to or from the cylinder is controlled. The governor 0 membrane is preferably of: a multicellular conrneability may bevaried. In" a typical-construction," for exampleya cellular sponge like' rubber may be employed as the "membrane, and the permeability of the membrane-may-be adjusted very easilyby altering the degree of compression to'whichitis subjected. Thedensity-'ofthe'mem- "brane determines its permeability by the-fluid,

and"therefore,'-controls the rate of-movement of the control fluid.

In previous constructions-such as -"theone 59 shown inFlarsheim Patent'No. 1,945,499, speed governors embodying hydraulic cylinders have been employed, the rate at which hydraulicfi'uid 'is permitted to escape being adjustable by means of an orifice or escape port of variable size. "It

"isapparent that very precise machining'of the parts is required toyproduce a satisfactory mechanism of this type, since any size imperfections,

' burrs-or surface variations arecapable of causing appreciable variations in the net sire of the 60 orifice. Ifdirt or gum lodges inthe or'iflceythen the apparatusbecomes out of adjustment. Also, even the air entrained in hydraulic fluid iscapable'of causing appreciable variations in performanee because of the compressibility-factor which is introduced by itspresence, and for that reason a bellows mechanism was additionally employed in the construction of the aforesaid Liebel "patent.

Previouspneumatic apparatus, on"the other hand, has been unsatisfactory-because the lodgment of dust or dirt *ina tinyairescape port causes the apparatus to' vary widely in performance, and, or course, it is virtuallyimpossibleto'exclude dust "from: a mechanism-of :this

4 type. In the present construction, on the contrary, the net orifice opening through which air movement is controlled is constituted by a multiplicityof tiny cells, passageways or interstices in the membrane, and the clogging of any one of them has no consequential effect upon the func- .;tioning of those remaining open. "Therefore, the

apparatus operates satisfactorily and consistently under the most adverse dust conditions.

-' Through filtering action of the diaphragm, dust particlescaught and retained in its cells may gradually tend to clog it over a long period of utime; H'oweverpwhen the diaphragm becomes too clogged to give satisfactory results, it may conveniently be: replaced by a new diaphragm.

The compressibility through which permea- 1=bi1ity=or .rate of fluid flow is varied is obtained conveniently by mounting the diaphragm between perforated plates, one of which is movable so that the diaphragm between them may be subjectedtozmore or less compressionrasdesiredi In this manner 'the 'apparatus .may be set initially rtosprovide any desired: rate of travel .under a "given motor mechanism force.

As explained more fullyin PatentNo. 2,591,936

on Reciprocating Bucky Diaphragm? it: isihighly desirable to construct a Bucky diaphragm so thatit willmove at a." constantspeed'in-one direction and then at a constant, 'butmuch-lower speed, in the opposite direction. By arranging "the diaphragm so that it always moves initially in the direction of higher'speedy'it isxpossible to prevent grid lines ona shortexposureas well as on'longer ones. It is another object ofthe present invention therefore, to provide aBuckydiaphragm actuator'in'cluding a fluid damping cylinder which is provided with two-governors; one of which-is efiectiveto controlthe rate piston move- 'ment-in one direction, the other being effective-to control the rate of movement in the opposite direction. The governors areso constructed that "the diaphragm travels in one direction-at a substantially higher speed than it travels in the op- "positedirection. Both governors may be of the porous type, or, as in the preferred embodiment disclosed hereingone governor of the porous type may be combined with another kind of governor. Whilethis invention is disclosed principally in "connection with reciprocating diaphragm actuators, it'will be understood that the principles'of this invention may also be'employed in a diaphragm actuator of the single stroke type.

These and other advantages of the present inventionwill be apparent from a considerationof the following detailed description of the drawings illustrating a preferred embodiment of the invention.

In the drawings:

Figure 1 is a general top plan view of a reciprocating' Bucky diaphragm provided withan' ac- Jtuator of the present invention.

= shown in Figure 1, both of the valves being shown in section to .illustrate detailsof the valveaction.

Figure 8 is a cross. sectionalt view similar to Figure '7 showing: the valveaaction as the piston cylinder: moves in opposite direction.

FigureB is: an enlarged longitudinal cross section'aliview' of the low spiced valve.

Figure I a graph showing: the relationship of grid position and'timer A reciprocating diaphragm: provided. with an actuator'of this. invention is shown in. Figure 1. The apparatus includes a 'rectangularsheet metal housing [0, a grid ll disposed for. sliding move:- ment within. the housing and an actuator mechanism indicated generally at ['23. The actuator includes asolenoid orthrustor mechanism I13: for moving: the grid in. one direction and a spring M for moving: it in: the opposite. direction. To:- pr 1- vide for continuous reciprocation. throughout an exposure. period, an electrical circuit of the type generally disclosed in Patent No. 2,591,536 .may be. electrically connected to the solenoid for alternately energizing and deenergizingit. This electric circuit incl'ud'esa switch I 5 actuated by movement of the grid structure and: arranged to deenergize the solenoid each time the gri'dtreaches the end of its travel toward: the right; Also in series with thereversing'switch is a control switch (not shown) manipulated by an operator or by mechanical or electric timer to control the length of time during. which the diaphragm. will continue to reciprocate.-

So long as this control switch is closed, the grid will continue to reciprocate; moving toth'e rightwhenever the solenoidis energized and moving. in the opposite direction under the influence of the spring tension whenever thesolenoid is deenergized. The rate of diaphragm movement in either direction is controlled by a damping cylinder, indicated; generally at l6, and" including valves [1- and H32 Thed'amping cylinder L5 may be mounted inany convenient manner upon housing [0, or, as in the preferred embodiment, the dampingcylind'er may be secured directly to solenoid l3, and contains a reciprocating piston which is secured to the grid structure H.

The Buck-y" grid itself includes the usual plurality of vertically disposedlead strips, delineating. slits through which X-rayspasstothe photographic plate; the exact. diaphragm structure is not-illustrated and in fact this invention maybe used with: any diaphragm which is effective to prevent secondary radiation from striking the photographic plate. The diaphragm is slidably mounted within a marginalframe 2 I-', preferably formed of channel shaped strips 22 joined to gether at the" corners. The forward edge 23 of the grid assembly l l carries bearing blocks 24 which are slidably mounted on apair oi-"rods Z5.

Rods 25' are supported by u -shaped brackets- 2B which are; in turn, secured; as byspot welding, to bar 21 extending transversely" of the housing I0". Set screws-28 areprov-ided fbr fastening the rods within apertures provided in the brackets 26. The rearward edge of diaphragm M isreciprocally supported by' bearing blocks 30"; engaging rails 3| which are supported fromiiame I 0 by means of brackets 32. Thus bearing blocks 2% and 30 support the Bucky diaphragm relative-to housing" l0 and permit it-to be reciprocatedtransverselywith respect to thehousin'g.

The exact construction of solenoid l3 c'onsti tutes no part of the present invention, since any of a number of commercially availablesolenoids may be employed; Generally, however, the solenoid includes a wound coil disposed within: a housi'ng 33 which is mounted' in any suitable manner 6 upon: thehousing' 1a. A plunger: 210: is reciprocall'y mounted. within'ethe: central opening: 34 of the: solenoid 0011;. '1l 1e=plungeris.= joined to" the diaphragm by means of. a. bracket 35 which is carried. by bearing blocks 24'. Bracket 35 includ'es an: extension 36 to which the: plunger wisjoined as by' bolt: 3T. Bearing rollers 38 forv guiding plunger zll' are mounted upon the solenoid housing 33 by'meansof'brackets 4 0-. and bolts 41?. The solenoid when energized. is effective to cause: the plunger 20' to move' to the: right',.in turn causing the movement of the entire diaphragm structure.

Spring; [4- is also connected to the diaphragm frame H, the spring being; placed. intension by diaphragm movement: to the right. As shown particularly in Figure 2 oneend 42 of spring I4 is looped and: 'engagesia suitable opening left hand bracket' 26 l he other end 43* ofthe spring is looped around an: extension 44 on' bearing; block 24. The springv is in. a condition of maximum tensi-onwhen the diaphragnrreaches the limit of its travel to the right, and: causes'reversali of the diaphragm almost assoorr as the solenoid is deenergized; Travel oi1the diaphragm to thezleftris governed: by the position of stops 45 mounted uponthe left hand edge: of housing l0" and: disposed'for'engagement with: frame I l: of the-Bucky diaphragm.

Control of the. rate of Buck-y movement is-exercised by damping cylinder: l6; which is: axialiy aligned with the central opening: the: solenoid housing and is joined to the housing by meansof bolts 4 6- engaging flange 41? of the cylinder; At one end. the damping cylinder is" provided: with an aperture for receiving the solenoid plunger. Preferably the: apertureis substantially larger than the: solenoid plunger so" that air can freely enter or leave this end of the cylinder; A. piston head 48E resides: within: cylinder. l 6. and is: secured to the end of solenoidplunger 20rbymeans of bolt 50a The pistonhead maybe of any type adapted for air-tight engagement with the cylinder wall, andi as shown. includes discsi5'l and 52 and packing members such: as leather cups 53' which fit between discs 51 and'i 52- and central disc 541 The endv of cylinder. 1J6 remote from the'solenoid housing is: fitted. with two: valves? I21 and. I8 for cont-rolling the rate of admission: andrescape ofair from cylinder IBi. Since piston. 4:8 com:- presses the airwithin cylinder I26 when the piston movestmthe right and creates-a vacuum when it moves to the: left, pistonmovement is impeded by an amount dependent upon the rate: at-which air can enter or'l'eave' cylinder I 6. through valves ll and [8. Valve lrl controlsthe escape of airfrom the cylinder andconsequ'e'ntly regulates the move:- ment of the Buckydiaphr-agmto the'right under the infl-uen'ce of solenoid energizationz Valve H3 controls the admission. of air: to the cylinder and consequently regulates the'rate of Bucky movementtothe le'ft under. the influence of spring: M.

More particularly; valves 1 l and lit are threadedinto-end member 55 which is secured as by welding to the end of the casingand" is held in place by flange 41 High speed valve l'lin cludesa casing. 56 configurated toform a longitudinal" passageway 515 and an enlarged open portion 58= forming a seat 60 for cooperation with needle valve 61 Needle valve-6 is threaded into the end ofopening 58 and is held in position by' means ofnut- 62-2 'I-hreadimgthe nee'dle'valve' inwardly or outwardly decreases or increases the rate atwhich air can pass between the needle valve 611' and seat. '60- and through passageway 511? and; opening: 631. A. second enlarged chamber 64 is provided for receiving the check valve 65 which functions to close valve II completely to the flow of air into the cylinder. The check valve structure includes a disc 66 mounted between plates 61 and 68. Plate 61 is provided with a central aperture 10 of a diameter smaller than disc 66. Plate 68 is provided with a series of peripheral apertures, some of which are disposed so that they are not closed by disc 66 even when the disc is in a position abutting the plate. The check valve functions so that when the piston is moving to the right and the pressure inside the cylinder is higher than it is outside, disc 66 is moved from a position covering the central aperture in plate 61 to a position abutting plate 68. In this latter position air can flow from the cylinder through the central aperture in plate 61, through the peripheral apertures in plate 68 and then through passageways 51 and 63 into the atmosphere.

The setting of needle valve 6| regulates the rate of flow of air from cylinder I6, and hence the rate at which the piston can be moved by the solenoid toward the right hand end of the cylinder. However, when the piston is moving toward the left, the lower air pressure within cylinder I6 causes disc 66 to shift to a position covering central aperture I of plate 61. In this position the disc prevents air from entering the cylinder through valve II so that only valve I8 exercises control over piston movement to the left.

Low speed valve I8, in the embodiment disclosed, functions to control the inlet of air to cylinder I6 whenever the Bucky diaphragm and. piston are moving to the left under the influence of the tension of spring I4. As previously explained, when used in conjunction with a reciprocating Bucky diaphragm, it is highly desirable that the piston move to the left at a lower rate of speed than to the right. Consequently, valve I8 should admit air to the cylinder I6 at a substantially smaller rate than it escapes through valve II when the piston moves to the right. Valve I8 thus must present a high resistance to air flow; but for any given setting of the valve, the resistance should remain substantially con stant and should not be appreciably affected by the accumulation of dust particles. I have found that a high resistance to air flow may be obtained by constructing valve I8 so that it presents a multiplicity of minute air paths rather than a single path of larger size.

More particularly, valve I8 includes a housing II which is threaded into end plate 55, the housing is provided with an axial chamber I2 and a small passageway I3 interconnecting the chamher and the interior of cylinder I6. Opening 14 vents chamber I2 to the atmosphere, the end of the chamber remote from the cylinder being closed by a threaded plug I5. Plug 15 is also threaded interiorly to receive threaded rod I6. Rod I6 is provided with a perforated plate 'II disposed at one end of the, rod in abutment with cellular member 18. Cellular member I8 forms a large number of small passageways through which air may pass through the member. The member I8 may be constituted by any suitable type of material; sponge rubber having been found very satisfactory. In the embodiment shown, the cellular member includes four discs of rubber which are compressed between plate I1 and a wire disc 80, residing against shoulder 8I formed at the end of chamber 12.

The cellular member I8 provides a very large number of air passages from passageway 'I3'to chamber 12, the resistance of these passageways offer to air flow is determined by the density of the cellular material, which in turn is affected by the degree to which it is compressed by perforated plate 11. Consequently, flow of air through the valve can be accurately regulated by tightening or loosening threaded rod I6.

When the piston head is moving from right to left, the pressure within cylinder I6 is less than the pressure of the atmosphere and disc 66 is forced against plate 61 covering the central aperture I0 to prevent any entrance of air into the cylinder through valve I'I. Consequently, the return movement of the Bucky diaphragm is controllably retarded solely by the amount of air permitted to enter chamber I6 through valve I8 and relieve the pressure in space 82 behind the piston.

Obviously, the damping cylinder and valves can be arranged in a number of ways, for example, so that valve I8 governs the escape of air from the cylinder and valve I'I controls the intake of air to the cylinders. Also it is possible to employ a multicellular construction such as is utilized in valve I8 for the high valve, or for both the low and high speed valves.

When the control switch in the solenoid energization circuit is depressed, the grid, which always starts an exposure period from its extreme left hand position, starts to move to the right due to the attraction of the solenoid coil. As shown diagrammatically in Figure 10, the diaphragm moves relatively rapidly to the right, slowing down only slightly as it approaches its extreme position indicated at 88 where it reverses its direction of travel. Just prior to the point at which the diaphragm reaches this position, switch I5 is tripped to deenergize the solenoid thereby rendering spring I4 effective to return the diaphragm to the left.

Any suitable type of switch can be used to deenergize the solenoid at this point in the diaphragm travel, one effective type of switch being shown in Figure 1. As shown, a microswitch is provided with a spring finger 84 which rides against a cam plate 85, pivotally mounted upon housing Ill. The cam plate has an arm extension 86 disposed for engagement with either of two lugs 81 and 88 secured to bracket 96. Lug 88 is located so that just as the diaphragm reaches its extreme left hand position the lug comes into engagement with arm 86 of cam rotating the cam so that portion 90 depresses spring finger 84 to close switch I5. This energizes the solenoid conditioning the actuator for Bucky movement to the right. Similarly as the diaphragm approaches its extreme right hand position, lug 81 engages finger 86, rotating the cam so that flat portion 92 engages switch finger 86, allowing the switch finger to spring toward the cam thereby opening the switch and deenergizing the solenoid. This conditions the diaphragm for movement to the left under the influence of spring I4.

As the diaphragm starts to move to the left after deenergization of the solenoid, a vacuum is created in space 82 behind the piston, forcing disc 66 of valve I'I over aperture I0 and thereby preventing air from entering the cylinder through that valve. Low speed valve I8 thus controls the flow of air into the cylinder, and, since this valve presents a high resistance to air flow, a pressure unbalance is created on the piston head, retarding diaphragm movement to the left. This slower rate of movement is indicated diagrammatically 9 in Figure 10 by the portion of the curve marked 93.

Having described our invention we claim:

1. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising, a motor mechanism for providing an actuating force in one direction, a cylinder having a piston in connection with the motor mechanism to provide a counteractive force, the said cylinder and piston mechanism having a fluid outlet, and a governor for controlling the rate of passage of fluid through said outlet comprising a porous cellular diaphragm disposed within said outlet and being adapted for fluid flow therethrough, the fluid within said cylinder acting upon said piston to provide a force counteractive to said actuating force.

2. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising, an electric solenoid having a movable plunger, a cylinder and piston damping mechanism in connection with said plunger for providing a force counteractive to the thrust of said plunger, and a fluid circuit in communication with said damping mechanism having a governor member in the form of a porous diaphragm disposed Within said fluid circuit and adapted for fluid flow therethrough, said diaphragm being effective to control the extent of counteractive force provided by said damping mechanism.

3. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising, motor mechanism for exerting a force in one direction, fluid damping means in connection with said motor mechanism for exerting a counteractive force in an opposite direction in consequence of motor actuation said damping means includes a fluid circuit, and a governor member for controlling the degree of counteractive force exerted by said fluid damping means, said governor member including a porous cellular member in said fluid circuit of the damping means for impeding the flow of fluid in said damping means.

4. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising, a cylinder having a piston therein and a valved inlet, a power actuator for moving said piston, said cylinder having an air outlet passageway through which air can escape in consequence of piston movement, and a sponge rubber cellular member, permeable by air, said sponge rubber cellular member being disposed within said air outlet passageway, to control the rate of air escape from said cylinder.

5. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising, a motor mechanism for providing an actuating force in one direction, a cylinder having a piston in connection with the motor mechanism to provide a counteractive force, the said cylinder and piston mechanism having a fluid passage and a governor for controlling the rate of flow of fluid through said passage comprising a porous cellular diaphragm residing within said passageway, the said porous cellular member being compressible, and means for compressing the said member to adjust its permeability with respect to flow of air therethrough.

6. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising, a cylinder havingv a piston therein and a valved outlet, a power actuator for moving said piston, said cylinder having an air inlet passageway through which air can enter in consequence of piston movement, and a sponge rubber cellular member, permeable by air in communication with said inlet passageway to control the rate of air admission to said cylinder.

7. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising a motor mechanism for providing an actuating force in one direction, spring means for alternately providing an actuating force in the opposite direction when said motor mechanism is rendered inoperative, means for rendering said motor mechanism alternately operative and inoperative, a cylinder having a piston in connection with the motor mechanism to provide a counteractive force opposing whichever of said actuating forces is causing diaphragm movement, the said cylinder and piston mechanism having two fluid valves including passageways communicating with said cylinder, at least one of said valves having a porous cellular diaphragm residing within said passageway.

8. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising a motor mechanism for providing an actuating force in one direction, spring means for alternately providing an actuating force in the opposite direction when said motor mechanism is rendered inoperative, mean for rendering said motor mechanism operative and inoperative, a cylinder having a piston in connection with the motor mechanism to provide a counteractive force opposing whichever of said actuating forces is effective to cause diaphragm movement, the said cylinder and piston mechanism having two fluid valves including passageways in communication with said cylinder, at least one of said valves having a flow controlling porous cellular diaphragm disposed Within its passageway, and means for adjustably compressing said porous cellular diaphragm for varying its resistance to fluid flow whereby the magnitude of said counteractive force can be regulated.

9. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising a motor mechanism for providing an actuating force in one direction, means for providing an actuating force in the opposite direction when said motor mechanism is rendered inoperative, means for rendering said motor mechanism operative and inoperative, a cylinder having a piston reciprocably mounted therein, said piston being in mechanical interconnection with said diaphragm and being effective to apply a counteractive force thereto in opposition to whichever of said actuating forces is efiective to cause diaphragm movement, said cylinder and piston mechanism having a first and a second fluid valve therein, each of said valves including a passageway communicating with said cylinder, said first valve being open at all times to permit fluid flow therethrough, said second valve being open to permit fluid flow therethrough when the piston is moving in one direction but being closed to fluid flow when the piston is moving in the opposite direction, said first valve including a porous cellular diaphragm residing in fluid connection with said passageway and presenting a higher resistance to fluid flow than said first valve.

10. An actuator for a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprisinga motor mechanism for providing an actuating force in one direction, a cylinder having a piston reciprocably mounted therein, said piston being in mechanical interconnection with said diaphragm and being effective to transmit thereto a counteractive force, said cylinder and piston mechanism having a valve therein, said valve including a fluid passageway in communication with said cylinder, and a porous cellular diaphragm residing within said passageway, the resistance to fluid flow of said cellular member resulting in a pressure unbalance on opposite sides of said piston to provide said counteractive force.

11. An-actuatorfor a diaphragm for screening secondary X-ray radiations from a photographic film, said actuator comprising a motor mechanism for providing an actuating force in one direction,a cylinder having a piston reciprocably mounted therein, said piston being in mechanical interconnection with said diaphragmand being effective to transmit thereto a counteractive force, said cylinder and piston mechanism havinga' valv therein, said valve including a fluid passageway in communication with said cylinder, and'a porous cellular diaphragm residing within said passageway having a resistance to fluid flow which is suflicient to provide a pressure unbalance on opposite sides of said piston and means for adjustably compressing said porous member to alter its resistance to air flow, thereby changing the magnitude of thecounteractive force.

12. An actuator for a diaphragm for screening x-ray radiationsi from.- a: photographic film said actuator comprising a motor mechanism for providing ran actuating' force in one direction, a. cylinder having ,a piston: reciprocably mounted therein, said piston: being in mechanical-interconnection with said diaphragm and being adapted to transmit a counteractive'torce thereto said cylinder and piston mechanism having'a fluid valve, .saidsvalve being provided-with a fluid passageway communicating with thein terior ot said cylinder, a porous cellular diophragm disposed: within said passageway and presenting. a resistance tdthe flow-of fluid therethrough,.. a "stationary apertured: memberl'abutting ones surfaceo! .aaid diaphragm a movable apertured member abutting th opposite ourface of said diaphragm, means do! adjust ably positioning said movable apertured member for compressing said poronstzcellular diaphragm to vary the resistance roflerediby-ssaid diaphragm .to -fluid flow through .ssaid. pmsageway.

liefcrlmees Cited ,in the .file, of: this patent UNITED STA'I'ES--PA'I'ENTS' Number Name Date 1,464,478 Greenwood Aug. 7,. 1923 1,508,391 Greenwood Sept.'-16,.l924 1,945,499 lFlarsheim .Jan. 30, 1914 2,077,295 Whitney Apr. 13, 1937 2,147,601 Flarsheim Feb. 14,1939 2,309,499 Chenault Jan, 26, 1943 2,591,536 Gieringer et.a1 Apral, 1952 

